调整 QListView 的高度以适应内容

Question

I want the height of a QListView based on an QAbstractListModel to fit the contents, if the amount of the items is smaller a given number N. If there are more than N items, it should show only N items. I read a lot of curious tips in the web, but most of them look like hacks. I guess this has something to do with sizeHint() but in the model view approach there is no ItemWidget in which I could override the sizeHint() . What is the correct way to achieve this behaviour?

Further, how does this correlate to the size policy of the parent app? This is a second constraint: The contents should not try to use the space they have in the parent widget, but the parent widget should resize to fit the QListView .

This is not a duplicate to this question , since I can't use QCompleter .

Answer 1

sizeHint() has to be overridden in the QListView (respectively your subclass of it). The mentioned special behaviour can be implemented there. eg like this:

QSize ProposalListView::sizeHint() const
{
    if (model()->rowCount() == 0) return QSize(width(), 0);
    int nToShow = _nItemsToShow < model()->rowCount() ? _nItemsToShow : model()->rowCount();
    return QSize(width(), nToShow*sizeHintForRow(0));
}

This requires the size hint of the item delegate to be reasonable. In my case:

inline QSize sizeHint ( const QStyleOptionViewItem&, const QModelIndex& ) const  override { return QSize(200, 48); }

Now I just have to call updateGeometry() after changing the model.

Answer 2

For those who use ListView in QML with QtQuick Controls. I made the content fit with property anchors.bottomMargin.

anchors.bottomMargin: 20

Answer 3

There is no good way to do this. I use the following code.

Header:

class List_view_auto_height : public QObject {
  Q_OBJECT
public:
  explicit List_view_auto_height(QListView * target_list);
  void set_max_auto_height(int value);
  void set_min_height(int value);

private:
  QListView* list;
  QTimer timer;
  int _min_height;
  int _max_height;

  bool eventFilter(QObject* object, QEvent* event);

private slots:
  void update_height();
};

Source:

List_view_auto_height::List_view_auto_height(QListView *target_list) :
  QObject(target_list)
, list(target_list)
{
  _min_height = 0;
  _max_height = 250;
  connect(list->model(), &QAbstractItemModel::rowsInserted,
          this, &List_view_auto_height::update_height);
  connect(list->model(), &QAbstractItemModel::rowsRemoved,
          this, &List_view_auto_height::update_height);
  connect(list->model(), &QAbstractItemModel::layoutChanged,
          this, &List_view_auto_height::update_height);
  list->installEventFilter(this);
  update_height();
  connect(&timer, &QTimer::timeout, this, &List_view_auto_height::update_height);
  timer.start(500);
}

void List_view_auto_height::set_max_auto_height(int value) {
  _max_height = value;
  update_height();

}

void List_view_auto_height::set_min_height(int value) {
  _min_height = value;
  update_height();
}

bool List_view_auto_height::eventFilter(QObject *object, QEvent *event) {
  if (event->type() == QEvent::Show) {
    update_height();
  }
  return false;
}

void List_view_auto_height::update_height() {
  if (!list->isVisible()) { return; }
  int height = 0;
  if (list->model()->rowCount() > 0) {
    height = list->visualRect(list->model()->index(list->model()->rowCount() - 1, 0)).bottom() + 1;
    height -= list->visualRect(list->model()->index(0, 0)).top();
  }
  if (list->horizontalScrollBar()->isVisible()) {
    height += list->horizontalScrollBar()->height();
  }
  bool scrollbar_enabled = false;
  if (_max_height != 0 && height > _max_height) {
    height = _max_height;
    scrollbar_enabled = true;
  }
  if (height < _min_height) {
    height = _min_height;
  }
  list->setFixedHeight(height + 6);
}

Usage:

new List_widget_auto_height(list);

It's full of hacks and can work incorrectly in some cases. Feel free to improve it.

It sets height using setFixedHeight . This should provide correct behavior for parent widget's size hint.